Vehicle locating systems which automatically determine and make available to a central point, the positions of a group of vehicles throughout a geographic area have been based on four basic techniques: radio propogation time, proximity, dead reckoning and triangulation. However, each has disadvantages particular to the technique which has heretofore made automatic vehicle locating systems impractical.
Optical systems, such as those for sensing the motion of railroad cars past a given location have been successful but are too expensive to use when a large number of locations are to be reported for a given vehicle rather than a large number of vehicles for a given location. Also the railroad systems can not accommodate the spacing and height differences that occur when automotive vehicles are to be located.
The need for automatic vehicle monitoring systems has been increasing for vehicles such as transit buses, police vehicles and taxi fleets as well as commercial users such as package delivery services and private maintenance and home repair services. More specifically, automatic vehicle locating systems offer means for dealing with the schedule variations of transit buses by applying real-time control to the systems. With the location of each bus continuously available to the central office, schedule deviations can be computed automatically and through a return radio link, drivers can be instructed to skip a stop, wait at a stop or take other corrective action to rapidly alleviate the schedule deviation. In addition to reducing routing and schedule deviations, automatic vehicle locating systems can enable buses to be rescheduled or re-routed quickly in response to unusual conditions such as traffic emergencies or bus breakdowns.
With police vehicles normally assigned to specific control areas, there are fixed protocols that govern their response to a crime. The ability of an automatic vehicle locating system to pinpoint the location of a car can enable the police dispatcher to assign the police car closest to the location of the crime. This not only can save time in responding to a call but it also can allow the selection of a cruiser, that, although assigned to an adjacent patrol area, happens to be closer to the problem and is available to respond faster. This same general approach can be used in taxi fleets to assure that the closest available taxi is alerted in response to a call for service thereby significantly reducing the amount of non-revenue miles for the taxis.